The present invention relates to a hydraulic lock device in which an elastically deformable sleeve is elastically deformed by oil pressure to lock a rod. More particularly, the present invention relates to a structure in which high oil pressure is created by a pressure booster in a casing member to elastically deform the sleeve.
A conventional hydraulic lock device, supporting a work by clamping or locking the work in an arbitrary position, is used when the work is cut or the like. Such hydraulic lock devices are disclosed, for example, in Japanese Published Unexamined Utility Models 59-128902 and 6-47710.
Japanese Published Unexamined Utility Model 59-128902 discloses a hydraulic lock device comprising a substantially cylindrical casing member, a hollow piston member slidably fitted into the casing member and designed to be elastically deformable to a smaller diameter, and a rod slidably fitted into the piston member and designed to pass through the casing member. This hydraulic lock device allows the piston member to be elastically deformed and pressed against the rod by the introduction of oil into a hydraulic chamber between the casing member and the piston member. In this state, the piston member and the locked rod prevent relative movement in the axial direction.
Japanese Published Unexamined Utility Model 6-47710 discloses a hydraulic lock device comprising a hydraulic cylinder having a cylinder main body and a piston member slidably fitted thereinto. A rod, passing through the cylinder main body, is inserted into the piston member while allowed to move axially in relation thereto. An elastically deformable sleeve is fitted over the rod between the piston member and the rod and mounted on the piston member while prevented to move in the axial direction in relation thereto.
This hydraulic lock device is operated when pressurized oil is introduced into the hydraulic chamber formed around the sleeve (which is part of the piston member). The sleeve is elastically deformed, pushed against the external peripheral surface of the rod, and locked to prevent the rod from moving relative to the piston member.
The present applicant has previously proposed a smaller hydraulic lock device capable of delivering higher output and using a smaller, lower-pressure hydraulic supply source. This hydraulic lock device is configured such that the interior of the casing member is provided with a pressure booster whose discharge portion is connected to an external hydraulic chamber, the external hydraulic chamber is sealably filled with oil, the pressure booster is actuated by the oil pressure input, an oil pressure greater than the oil pressure input is generated in the external hydraulic chamber, and the thin-walled cylindrical portion of the sleeve is deformed to a smaller diameter, thereby locking the rod. Another feature of this structure is that pressurized oil is fed through a single pressurized oil feed port to a rod-moving hydraulic cylinder. The pressurized oil is then guided into an oil channel passing through the input oil chamber of the pressure booster. The rod is locked by the pressure booster after being moved and pressed against the work by the rod-moving hydraulic cylinder through the use of the oil pressure input from the pressurized oil feed port.
The hydraulic lock devices disclosed in Japanese Published Unexamined Utility Models 59-128902 and 6-47710 are configured such that a sleeve separate from or integral with a piston member is elastically deformed by oil pressure to a smaller diameter. A rod is then locked by a static friction force acting between the sleeve and the rod.
With this structure, the locking force decreases when low oil pressure is used to elastically deform the sleeve. In view of this, a larger locking device is needed in order to generate a more powerful locking force, creating disadvantages in terms of equipment costs. Alternatively, high oil pressure must be obtained from the hydraulic supply source, making the hydraulic supply source bulkier, increasing the likelihood of hydraulic leaks, and incurring higher costs.
The hydraulic lock device of present applicant is configured with pressurized oil concurrently fed to the rod-moving hydraulic cylinder and the pressure booster through a common pressurized oil feed port. This, however, sometimes causing the pressure booster to start operating and to lock the rod while the rod has not yet attained sufficient mobility (that is, the rod has not yet come into contact with the work). This results in unacceptably low operating dependability or reliability.
It is an object of the present invention to provide a hydraulic lock device which overcomes the foregoing problems.
It is another object of the present invention to provide a hydraulic lock device with high dependability and reliability, reducing the size and increasing the output of the devices, and reducing the size and increasing the pressure of hydraulic supply sources.
The hydraulic lock device of the present invention comprises a rod as an output member, a sleeve with a thin-walled portion fittable over the rod and elastically deformable to a smaller diameter, a casing member for supporting the sleeve, and an external hydraulic chamber formed around the sleeve. This hydraulic lock device is characterized in that a rod-moving hydraulic cylinder is provided for moving the rod in the direction of the axial center. The interior of the casing member is provided with an annular pressure booster for pressurizing the oil in the external hydraulic chamber. The casing member is provided with a pressurized oil feed port for feeding pressurized oil to the rod-moving hydraulic cylinder and the input oil chamber of the pressure booster. A throttle valve is interposed in an oil supply channel extending from the pressurized oil feed port to the input oil chamber. An oil discharge channel, extending from the input oil chamber to the pressurized oil feed port, is provided with a nonreturn valve capable of discharging pressurized oil from the input oil chamber. The nonreturn valve is opened when the pressurized oil is discharged through the pressurized oil feed port.
The following is a description of a case in which a work to be machined is supported from below by a hydraulic lock device. The work is delivered to a point above the hydraulic lock device, and pressurized oil is fed from a hydraulic supply source to the pressurized oil feed port, whereupon the rod-moving hydraulic cylinder is actuated and the rod is moved upward. Pressurized oil is gradually fed, in a parallel fashion, to the input oil chamber of the pressure booster via the throttle valve. The pressure booster is actuated after the rod has completed its movement (that is, has come into contact with the work), and an oil pressure higher than the input oil pressure is generated in the external hydraulic chamber outside the sleeve. The thin-walled cylinder of the sleeve is thereby elastically deformed to a smaller diameter, securely locking the rod. The pressure booster is actuated by the pressurized oil input, and the oil inside the external hydraulic chamber of the sleeve is pressurized, making it possible to design a more powerful locking device without increasing the size of the device. Additionally, the hydraulic locking device of the present invention requires a more compact hydraulic supply source capable of operating at a lower pressure.
When, for example, the valve of the hydraulic supply source is switched and the pressurized oil is discharged through the pressurized oil feed port as the rod is returned to its original position after the work has been machined, or the like, the nonreturn valve is opened and pressurized oil is discharged from the input oil chamber of the pressure booster into the pressurized oil feed port via the oil discharge channel. As a result, the pressure booster returns to its original state, the thin-walled cylinder of the sleeve is expanded again, the locked state of the rod is canceled, and the rod is moved downward (for example, manually) while the drain-pressure oil of the rod-moving hydraulic cylinder is discharged.
In particular, the presence of the throttle valve in the oil feed channel between the pressurized oil feed port and the input oil chamber makes the rod-moving hydraulic cylinder operate more quickly than the pressure booster. This makes it possible to lock the rod after it has moved a sufficient distance (that is, has come into contact with the work) and allows the hydraulic lock device to operate with higher dependability and reliability. The presence of the nonreturn valve, which is opened when pressurized oil is discharged from the pressurized oil feed port, allows the pressure booster to be returned to its original condition with greater speed.
The throttle valve arrangement of the hydraulic lock device may be replaced with an arrangement in which an oil channel, extending from the pressurized oil feed port to the input oil chamber, is provided with a sequence valve that is opened against the elastic force of a valve-closing spring after the oil pressure inside the pressurized oil feed port has risen to a prescribed level. An oil discharge channel, extending from the input oil chamber to the pressurized oil feed port, is provided with a nonreturn valve capable of discharging pressurized oil from the input oil chamber. The nonreturn valve is opened when the pressurized oil is discharged through the pressurized oil feed port.
Adopting a structure in which a sequence valve is provided to the oil channel between the pressurized oil feed port and the input oil chamber, and the valve is opened against the elastic force of the valve-closing spring after the oil pressure inside the pressurized oil feed port has risen to a prescribed level, allows the rod to be locked after it has moved a sufficient distance (that is, has come into contact with the work). Such a hydraulic lock device operates with higher dependability and reliability.
Incorporating the sequence valve into the valve body of the nonreturn valve makes it possible to simplify the structure of the hydraulic lock device, to reduce the required number of parts, to curtail the manufacturing costs, and to make the locking device more compact.
The sequence valve may also comprise a ball-shaped valve body and a valve seat formed in the oil channel (which extends from the pressurized oil feed port and the input oil chamber) and closed in conjunction with the valve body. The valve body is pressed against the valve seat, and the sequence valve is closed by the valve-closing spring and the oil pressure of the pressurized oil feed port when pressurized oil is fed through the pressurized oil feed port. When the rod is returned to its retracted position, the pressurized oil is discharged through the pressurized oil feed port, the valve body moves away from the valve seat against the urging force of the valve-closing spring, and the sequence valve is opened.
The pressure booster may also comprise a piston member for receiving pressurized oil from the input oil chamber and increasing the oil pressure of the external hydraulic chamber. The pressure-receiving area of the piston member on the side of the input oil chamber may be set greater than the pressure area facing the external hydraulic chamber. In this case, the oil pressure applied to the input oil chamber through the pressurized oil feed port is increased by the pressure booster in proportion to the pressure-receiving area ratio. The pressurized oil in the external hydraulic chamber is additionally pressurized to provide an enhanced pressurization effect on the external periphery, securely locking the rod.
The rod-moving hydraulic cylinder may also comprise a spring for elastically urging the rod toward an advance side such that the rod is driven to the advance side and pressed against the rod by this spring.
The rod-moving hydraulic cylinder may further comprise a return spring for urging the piston member to a retraction side, in which case the rod is returned to the retraction side by the spring after the lock on the work has been released.
The above, and other objects, features and advantages of the present invention will become apparent from the following description read in conjunction with the accompanying drawings, in which like reference numerals designate the same elements.